Conventionally, there have been cases where a stent which is formed from a metallic wire or the like in the shape of a hollow cylinder having a multiplicity of openings in its side wall and which is expandable in a lumen of a living body, such as a blood vessel, bile duct, trachea, esophagus and urethra, is used for improving a lesion part (stenosed part or obliterated part) in the lumen of the living body.
In the case of a self-expandable stent in which the stent itself has a self-expanding function, for example, there has been known a stent delivery system in which the stent is delivered into the living body in the state of being compressed and contained in a gap between an inner tube and an outer tube, and then the outer tube is retracted proximally so as to release the stent, whereby the stent is put indwelling (indwelled) in the lesion part.
As disclosed in Japanese Application Publication No. 2007-504897 (JP-T-2007-504897), for example, the above-mentioned stent delivery system has an operating mechanism for displacing the outer tube in an axial direction relative to the inner tube. In the operating mechanism, a gear rack is meshed with a gear of a rotatable wheel, and the outer tube is connected to an end portion of the gear rack. With the wheel rotated in a predetermined direction, the gear rack is advanced and retracted in the axial direction so as to move the outer tube relative to the inner tube, whereby the stent is released to the exterior of the outer tube.
In the stent delivery system having the operating mechanism as above-mentioned, however, the gear rack and the outer tube connected to the gear rack can be moved in the axial direction attendantly on the rotation of the wheel. Therefore, in the case where the outer tube is caught in the lesion part in a lumen of a living body or the like so that movement of the outer tube in the axial direction is made difficult, for example, if an operator continues to forcibly rotate the wheel, the gear rack and the outer tube are forcibly pulled in the axial direction. This is attended by exertion of an excessive load on the stent delivery system (especially, on the outer tube). As a result, the stent delivery system would be broken, so that a broken component part of the stent delivery system may be left in the lumen of the living body.